1. Field of the Invention
This invention relates to computer systems. In particular, the invention relates to memory devices.
2. Description of Related Art
A dynamic random access memory (DRAM) device is divided into banks where each bank consists of an array of memory cells plus a set of sense amplifiers for holding data. When the sense amplifiers of a bank contain valid data, the bank is referred to as “open”; otherwise, it is “closed”.
In conventional DRAMs, the bank structure is independent, i.e., each bank has its own complete set of sense amplifiers. This allows independent operation of the banks.
DRAMs may also have banks organized in a dependent manner. In this organization, adjacent banks share a portion of the sense amplifiers. Thus, when bank j is using the sense amplifiers, banks j−1 and j+1 cannot. In other words, when bank j is “open”, banks j−1 and j+1 are “locked” from being accessed. Banks j−1, j, and j+1 constitute a “bankset”.
The dependent structure of DRAMs presents a challenge to the design of the memory controller in a high performance microprocessor system. In addition, the memory controller should be able to work with DRAMs having mixed structures, i.e., some portions have dependent structures and some portions have independent structures. An intelligent memory controller should be able to track the state of all pages used within a memory system.
Existing memory controllers only deal with independent structures. Dependent structures introduce additional requirements and constraints on the mechanism to track page state.
Therefore there is a need in the technology to provide a simple and efficient method to track the state of a page in a memory device.